The present invention relates to a device for separating small drops of liquid from a flowing gas containing liquid mist, comprising a first container, formed of a cylindrical lateral wall and two opposite end walls, said first container having an inlet in one end wall for the gas/mist, a first outlet in its other end wall for the gas and a second outlet at or in the vicinity of the second end wall for liquid separated out of the gas, a second container with means for rotatably mounting the first container in the second container rotationally symmetrically in relation to said inlet and said first outlet, and drive means for rotation of the first container in the second container.
It is a known fact that it is not possible to achieve piston ring seals between the pistons and the surrounding cylinder walls of the cylinders in an internal combustion engine, which seal off the combustion chambers 100% against the engine crankcase. A certain small amount of combustion gases, called here blow-by gas, thus always flows past the piston rings and down into the engine crankcase. In order to prevent excessive pressure caused by the blow-by gas in the crankcase, the crankcase must be ventilated and the gas drawn off leaving only a low overpressure in the crankcase.
Two types of crankcase ventilation are used, viz. either open or closed ventilation. An engine with open ventilation can, quite simply, have a downwardly directed tube connected to the valve cover, for example, and which opens into the surrounding atmosphere. In an engine with closed crankcase ventilation, the blow-by gases from the crankcase are led to the engine intake conduit and are mixed with the intake air.
When evacuating blow-by gases, it has, up to now, been unavoidable that a certain amount of oil mist will accompany them. The amount of oil being carried with the gas depends on the placement of the ventilation outlet and any filters or oil traps in the crankcase ventilation. Regardless of whether the engine has open or closed crankcase ventilation, it is desirable to keep the amount of oil in the evacuated blow-by gas at a minimum. In the first case, it is to minimize the effect on the environment and to keep the engine oil consumption at a low level. In the second case, it is to prevent oil deposits on or in the components of the engine intake system, e.g. oil deposits on the impeller blades of the compressor of a turbo-charged engine or oil deposits in the charge air cooler in engines with charge air cooling.
A number of different devices to separate oil from blow-by gases from internal combustion engines are known. Among them are various types of baffle or screen systems, metal wire or textile fibre filters as well as cyclones and centrifuges. With the aid of baffle and screen systems, it has up to now been possible to separate oil drops down to a diameter of circa 10 xcexcm, with metal wire filters and cyclones down to circa 1.5 xcexcm and with multi-layer textile fibre filters, e.g. fleece filters, down to circa 0.4 xcexcm. Baffle and screen systems have, in principle, an unlimited lifetime and do not produce any pressure losses, but do not provide sufficiently effective oil separation, since circa 80% of the oil mass in the oil mist in the blow-by gases consists of oil drops with a diameter which is less than 1.5 xcexcm. Previously known metal wire filters and cyclones thus are not sufficient either for achieving effective oil separation despite the fact that they have acceptable lifetimes and provide limited pressure losses. Multi-layer fleece filters remain, but these have limited lifetimes and therefore must be replaced often, leading to high costs. They also produce significant pressure losses.
The purpose of the present invention is to achieve a device of the type described by way of introduction, i.e. a separator of centrifugal type, which is particularly, but not exclusively, intended for separation of oil mist drops from blow-by gases from internal combustion engines and which can separate liquid drops of less than 1 xcexcm without having the disadvantage of a multi-layer fleece filter, for example.
This is achieved according to the invention by virtue of the fact that the inlet and the outlets communicate with each other via a plurality of layers of peripherally spaced, narrow channels extending in the direction of the rotational axis and being disposed at a radial distance from the rotational axis, said narrow channels having a radial dimension being adapted to their length, their radial distance to the rotational axis, the flow velocity of the gas and the rotational speed, so that at least the major portion of the liquid drops in the mist will have time to be deposited on the channel walls before they reach the outlet.
Tests performed have demonstrated that in a preferred embodiment particularly designed for separating oil mist from blow-by gases, with a suitable selection of the above-mentioned parameters, more than 90% of all the oil mist in the gases was separated out. The gas velocity, the distance which the oil drops must move radially outwards to strike the channel wall, and the radial acceleration determine in this case the required length of stay for the drops in the channels. This length of stay determines in turn the required channel length. It has been shown that the diameter (of circular channels) should not exceed, but should preferably be less than 1 mm for the separator to have reasonable dimensions and a reasonable rotational speed.